1. Field of the Invention
This invention relates generally to a method and apparatus for recording and/or reproducing an analog signal and, more particularly, to a method and apparatus for recording and/or reproducing an analog signal as a pulse-code-modulated (PCM) signal incorporating error-correcting and parity information in which the time-base is compressed prior to recording and is expanded upon reproduction.
2. Description of the Prior Art
Recording and reproducing an analog signal, such as an audio signal, as a pulse-code-modulated (PCM) signal permits high-quality recording and reproduction. Both fixed-head and rotating-head systems have been used for recording and/or reproducing PCM signals, and the rotary head system of a video tape recorder (VTR) has been proposed to record an audio PCM signal. Typically, in a VTR having two rotary heads, the heads are located diametrically opposite on a rotating drum, that is, the heads are spaced 180.degree. apart and the magnetic tape is wrapped about the periphery of a tape-guide drum for an angular extent substantially the same as the head separation. Each head then traces or scans a track on the tape for each revolution of the drum. When the information signal is recorded by the rotary head on the tape in the form of an analog signal, in order to prevent signal dropouts, it is necessary that the rotary head recording the signal always be in contact with the tape. Otherwise, the signal would not be continously recorded. On the other hand, in the case of recording a PCM information signal, because the PCM signal is a digital signal the time-base thereof can be compressed and/or expanded in a straightforward fashion by the use of one or more digital memory units. An example of apparatus for recording and/or reproducing a PCM signal using a rotary head system is disclosed in U.S. patent application Ser. No. 06/485,065, filed Apr. 14, 1983 and assigned to the same assignee herein. In that application it is recognized that when the PCM signal is recorded by the rotary head with no dropouts in a fashion similar to an analog signal there is no time available in which to add redundant data, such as parity words or error check words, to the PCM signal. Accordingly, apparatus is disclosed that employs a system of buffer memories, random access memories, and appropriate switching networks to delay the signals to be recorded. This processing of the PCM signal to be recorded, while effective, is complex and cumbersome, as well as costly since it involves so many additional circuit elements. Nevertheless, time-base compression is necessary in order to provide the additional time within which to perform error detection and correction.
Along with all of these problems there is the further requirement that the rotary head and tape-guide drum subassembly be as small as possible, in order to promote the portability of the unit. A principal limiting factor on the minimum dimensions of a video tape recorder is the diameter of the tape-guide drum.